New COVID-19 FLiRT strain detected in Arizona. Here's what you need to know

A new set of COVID-19 subvariants has been significantly increasing in prevalence but the strains, known as FLiRT, are not expected to cause more serious illness than prior versions of the virus.

David Engelthaler, who leads the infectious-diseases division of the Arizona-based Translational Genomics Research Institute, says the FLiRT strains of the SARS-CoV-2 virus that causes COVID-19 are "definitely the latest sequel to omicron."

People at high risk should still be on alert, but FLiRT does not appear to pose a higher threat than other strains of the COVID-19 virus, he said.

There have been a "couple of instances of FLiRT variants" detected in Arizona but it's difficult to have a good gauge on how much is here because sequencing of the virus strains has significantly declined from the levels of sequencing that happened during the pandemic, Engelthaler said.

"We do know it's here. We've seen it and that's not a surprise," Engelthaler said of the FLiRT strains. "It is likely showing up in every state."

The U.S. Centers for Disease Control and Prevention is tracking the KP.2 and KP.1.1 strains of the COVID-19 virus, which are sometimes referred to as FLiRT, officials told The Arizona Republic in an email. KP.2 is right now the dominant COVID-19 variant in the U.S., but laboratory testing data indicate low levels of transmission of the virus at the moment, a CDC spokesperson wrote.

"That means that while KP.2 is proportionally the most predominant variant, it is not causing an increase in infections as transmission of SARS-CoV-2 is low," the spokesperson wrote. "Based on current data there are no indicators that KP.2 would cause more severe illness than other strains. CDC will continue to monitor community transmission of the virus and how vaccines perform against this strain."

Will FLiRT will cause a summer surge of COVID-19?

There is not enough evidence to say whether FLiRT strains will cause a summer COVID-19 surge, Engelthaler said.

The latest estimates from the U.S. Centers for Disease Control and Prevention say that the FLiRT subvariant KP.2 was 25% of the strains in circulation across the U.S. for the two-week period ending April 27, up from 11% from the prior two-week period ending April 13.

KP.1.1, another of the FLiRT strains, went from 3% of the estimated strains in circulation to 7.5% in the reporting period ending April 27, CDC data shows.

"Clearly it's becoming the more common set of variants that are out there now but it doesn't mean that we are really seeing increases in cases," Engelthaler said. "In fact, when you look at the numbers pretty much everywhere it looks like it is trending down. So this is just the most efficient version."

Similarly, Dr. Eric Topol, a cardiologist and executive vice president at Scripps Research who writes a popular newsletter about the latest COVID-19 research, on April 18 predicted that there could be a "wavelet but not a significant new wave of infections as a result of the FLiRT variants over the next couple of months."

Topol believes it will take a much bigger challenge to our immune response than what the FLiRT subvariants are showing to cause a big new wave, but "we can't necessarily count on that optimistic perspective" and "time will tell."

Why is it significant that FLiRT is related to the omicron variant?

Like other strains of the COVID-19 virus, the FLiRT versions are descendants of the omicron subvariant. Omicron subvariants have the same characteristics: They seem to spread easily and evade antibodies built up from vaccinations and previous infections which is why new subvariants keep emerging.

"It's a couple of variants that are additional subvariants of the original omicron," Engelthaler said of FLiRT. "This will likely spread around a little easier but right now we're not seeing any indications that it's causing a real uptick. It's possible we see that, but I don't know that that risk is very high."

FLiRT earned its nickname because of mutations in the spike protein on the COVID-19 virus, one where an F amino acid turned into an L and one where an R turned into a T.

"Pretty much every infection in the world and every form of this virus we see is all omicron, just different variants of omicron," Engelthaler said.

"It is possible that there are some that are circulating out in some animals. ... It could be a different version, a non-omicron version and that might be cause for concern and that is why we are continuing to test animals and watching this out in the environment, as well as seeing what is still spreading between humans."

Why is the COVID-19 virus still circulating?

The COVID-19 virus has settled into an evolutionary strategy, Engelthaler explained. The virus is making minor tweaks in the spike protein just enough to get away from the antibodies people have built up from the previous versions, he said, and that way it can survive and move around.

"This is still the same omicron virus. By and large for most people, it could be a nasty cold. Some people could still have a serious outcome from it, but those are the people that we know are the highest risk," Engelthaler said. "And if they haven't had a previous infection or vaccination or a recent one, they would be at higher risk."

Engelthaler compared the subvariants of omicron to the "Fast & Furious" action film franchise.

"Every six months it feels like there's a new sequel coming out. There's a bit of hype around it and it is a little bit different from the last one," Engelthaler said. "But in the end you really can't tell the difference between them and this is pretty much how this virus is going to keep moving around."

Reach health-care reporter Stephanie Innes at stephanie.innes@gannett.com or at 480-313-3775. Follow her on X, formerly known as Twitter, @stephanieinnes.